If two objects collide and the kinetic energy remains constant, the collision is termed perfectly elastic. Under these conditions, if an object of mass m₁ and initial velocity u₁ strikes a second object (initially at rest) of mass m₂ ,  such that the velocities after collision are v₁ and v₂ , the following equations are found:

Solve these equations for m₂ in terms of u₁, v₁, and m₁.

'n'ru mv + mv +mu = +mv + + mv/